Staring up at the night sky, you might see thousands of stars sprinkled above the horizon. It feels as though you can see so much of the universe beyond Earth; however, some of the most interesting aspects of space are hiding in the darkness between. Exoplanets, planets that exist outside of our solar system, can be discovered in the darkness if you know how to look.
David Martin, assistant professor in the Department of Physics and Astronomy, finds and researches such planets.
“I am an astrophysicist, primarily studying … exoplanetary systems,” Martin said. “I am a combined hybrid theorist observer … so I try to find new planets … and then I also do theoretical work to try to come up with ideas of how we explain how planets form and evolve.”
The field of exoplanets is very young, with the first exoplanet discovery occurring in 1992. Martin spoke to how he enjoys the field and community around it.
“It’s definitely captured the public’s attention, so there’s a lot of funding for it, there’s a lot of missions for it, there’s a lot of ability to reach students on it. So it’s a very vibrant field,” Martin said.
But how does one find a planet? While taking a direct image of an exoplanet has become possible at the cutting edge of recent technology, Martin uses two other methods to locate new planets. These indirect techniques are not as complicated as one might think.
“One [method] is you simply look at a star. You look at how bright it is over time … then if something passes in front of it, it gets dimmer, it’s just blocking it out,” Martin explained. “And if it’s a planet, it should come back on some periodicity. So if it were the earth, it would come back once a year.”
Using this method, researchers are able to track the temporary dimming of a star’s light and deduce if it is due to a planet passing in front. The other method used to find exoplanets involves looking at the quality of light coming from a star instead of the quantity.
“Stars produce light across a spectrum of colors, and different colors of light mean different frequencies of light,” Martin said. “If you’ve ever heard an ambulance going, you hear the Doppler effect, where the ambulance is a high pitch going towards you, and it’s a low pitch going away from you. We can see that in light as well. And so you can look at a star’s light and see how the color becomes a little more red or a little more blue as the star moves, and that movement would be due to a planet.”
Beyond just using these methods to find new planets, Martin specifically seeks out exoplanets that break the norm and push how we understand them. One notable example is that Martin researches exoplanets that orbit binary stars, like that of the fictional Tatooine in the Star Wars universe.
“Those systems, [binary stars], really do exist. And some folks, I guess not George Lucas, but some folks thought they might not exist. And so it’s been quite cool to find that they exist and are actually pretty common,” Martin said.
Martin explained that researchers have historically been able to find larger planets, the likes of Jupiter or Saturn, in binary star systems; however, finding smaller planets has proven much more difficult. This is because both methods of finding planets involve impacts on the light of stars, which is more obvious for bigger planets.
“So whilst we could find big planets, we haven’t yet been able to find small planets,” Martin stated. “That’s been my biggest mission over the past five years, to find those small planets, because I know they exist out there around single stars. Do they exist around binaries?”
In this vein, Martin has done theoretical work in which he produced papers arguing why small planets around binary stars might not exist. While this may seem in direct contradiction to his work looking for said small planets, he explained why finding that something doesn't exist can be more interesting than if it does.
“If we could show that small planets generally do not exist around two stars, but they are so common around one star, that means there’s a huge difference in how we form planets around one versus two stars, that is interesting. One might argue even a more interesting answer,” Martin said.
In the end, exploring the universe in search of undiscovered planets is a freeing experience. Martin explained that he wished people knew how science is a creative field that requires courage.
“The thing I wish folks knew most about scientific research is that, yes, you do need to have good technical skills and such, but I do think that the greatest successes come from when you are creative and sort of daring,” Martin said. “I feel like the fact that science is a very creative field sometimes gets lost.”
